The distribution and transportation of blood between different parts of the body is regulated by many physical factors, and the lack of knowledge with respect to venous flow and the behavior of venous valves has often made current treatment of venous disorders ineffective. In the last decade, a fair amount of attention has been given to difficulties that occur in circulation in humans that result from nonoperative or malfunctioning venous valves. Apparatus and medical procedures have been developed for excising such malfunctioning valves.
Venous valves act to assist the return of venous blood to the heart as part of the physiological pumping system known as the "venous pump" or "muscle pump". Venous valves are one-way valves arranged so that the direction of blood flow can only be towards the heart. Every time the legs are moved, or muscles tensed, a bolus of blood is propelled towards the heart. This bolus, moving towards the heart, opens and crosses a venous valve. Reverse flow is then prevented by the closing action of the venous valve. In the next movement or contraction, the venous blood bolus is lifted through the next venous valve and so forth until it has returned to the heart from the lower extremities via the venous or muscle pump. This venous pump is independent of the contraction of the heart.
Venous return from an extremity of the body is not actually dependent upon properly functioning valves when a patient is in the supine position because the existing pressure gradient to the heart may be sufficient to assure normal return. However, proper functioning of venous valves in the lower extremities can be of critical importance in minimizing pressure build up when the body is not in the supine position. Unfortunately, diagnosis of a problem with one or more venous valves has not been sufficient because there are currently no known commercially available prosthetic valves that can function satisfactorily as a replacement for a malfunctioning native valve.
Some relatively simple, experimental venous valves have been developed, such as those shown in U.S. Pat. Nos. 5,358,518, 5,500,014, and 5,607,465, and one somewhat more complicated venous valve implant is shown in U.S. Pat. No. 5,824,061. Moreover, a double-ball check valve and intraluminal graft is shown in U.S. Pat. No. 5,697,968, and a self-expanding poppet valve that can be inserted through a catheter while confined in a tubular sheath is shown in U.S. Pat. No. 5,397,351.
The potential for thrombosis at replacement venous valves is a very important consideration for, because of its very nature, the valve is always in contact with blood; thus, such must be given the utmost attention. As one alternative, devices have also been designed to simply bypass venous valves by holding them open, such as that shown in U.S. Pat. No. 5,843,171. In addition, devices have been constructed to test the operation of both artificial and natural venous valves, such as that shown in U.S. Pat. No. 5,272,909. However, despite the considerable work that has gone into this area, satisfactory solutions have not yet been achieved; thus, the search for more satisfactory prosthetic venous valves has continued.